Elsevier

Thin Solid Films

Volumes 377–378, 1 December 2000, Pages 602-606
Thin Solid Films

Nanotribology and surface chemistry of reactively sputtered Ti-B-N hard coatings

https://doi.org/10.1016/S0040-6090(00)01274-8Get rights and content

Abstract

The nanotribological performance of Ti–B–N protective coatings, 500 nm thick, have been studied in the range of 0–38.5 at.% N. A correlation was established amongst the chemical state, structure, mechanical properties, and nanowear resistance as a function of atomic percent nitrogen. The mechanical properties, elastic modulus and hardness, of the films were tested using a Hysitron Triboscope nanomechanical test instrument. The nanotribological performance of the films was evaluated using a Nanoindenter II with scratch capability. Single and reciprocating nanowear scratches, 10 μm in length, were performed at normal loads ranging from 50 to 750 μN. An atomic force microscope (AFM) was utilized to characterize the nanowear tracks with respect to depth and amount of plowing of material. The AFM images revealed that the reciprocating nanowear test caused grooving of the films with little to no material removal. Chemical and structural information was obtained by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Increasing N content correlated with increasing number of B–N bonds, structural disorder, and decreasing hardness, modulus, and wear resistance.

Introduction

Wear resistant coatings must exhibit high hardness and toughness in order to be able to protect the substrate from deterioration, in such applications as magnetic recording media [1]. Such coatings often serve more than one function, protecting the substrate not only from wear, but also from environmental effects such as corrosion/oxidation. Titanium diboride (TiB2) and TiB2(N) coatings are of interest in this context due to their high hardness, wear resistance, and corrosion resistance [2], [3], [4], [5]. Hardness values greater than 50 GPa have been reported for this class of coatings [6]. Small additions of nitrogen have been shown to increase the hardness of these films and to promote structural disorder [2].

In this paper the nanoscale wear resistance, as well as the surface chemistry of reactively sputtered TiB2(N) hard coatings, was reported. Assessing the resistance of the coatings to low load wear was the main thrust of the research. A statistically significant decrease in mechanical properties and wear resistance was observed with increasing N content.

Section snippets

Experimental

500-nm thick coatings were deposited on silicon (Si) substrates using a dc magnetron sputtering system from a 99.5% pure TiB2 target in argon (Ar) and argon/nitrogen (Ar/N) atmospheres to produce six different N content samples. The chamber pressure was held constant at 0.667 Pa while the gas flow rates of the Ar and Ar/N mixture were varied to control the N content in the chamber, from 0 to 20% N. The average deposition rate was 0.58 nm/s.

Nanotribology experiments were carried out on a

Results and Discussion

The surfaces of the samples were sputter cleaned in the XPS chamber prior to analysis. N1s, B1s, and Ti2p spectra were collected and the atomic concentrations of Ti, B, and N were determined from the areas underneath the spectra. The atomic concentrations of N in the six samples were; 0, 7.5, 13.5, 26.5, 32.5, and 38.5%. The evolution of the B1s spectra was the most revealing of the XPS data, and is shown in Fig. 1 for all six samples. The intense peak at a binding energy of 187.6 eV

Conclusions

The XPS results showed the formation of B–N bonds within the nitrogenated coatings, with a significant amount of B–N bonds in the three highest at.% N samples. The X-ray data revealed that the coatings became amorphous with the addition of nitrogen. From the multi-pass and single pass nanowear tests, the residual depths increased with increasing at.% N, meaning there were larger penetration depths in the coatings containing larger amounts of B–N bonds. The effect of the larger penetration

Acknowledgements

This work was supported by the U.S. Army Research Office under Grant No. DAAD 19-99-1-0152 and acknowledges the use of facilities supported by the MRSEC Program of the NSF under Award No. DMR-9809423.

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